1. Field of the Invention
The present invention relates to reduced smoke generating polyurethane/polyisocyanurate foams (PU/PIR foams) and the process for preparing such foams. Specifically the invention relates to PU/PIR foams having a Class I flame rating containing aliphatic dibasic esters as the smoke reducing agent.
2. Description of the Related Art
A critical factor in large scale commercial acceptance of rigid foams has been the ability to produce foams which exhibit low flame spread and smoke generating characteristics. In order to improve the performance of foams, aromatic polyester polyols have been used in the production of polyurethane foams and urethane modified polyisocyanurate foams. The use of such polyester polyols is described, for example, in U.S. Pat. Nos. 2,246,365 and 4,039,487. U.S. Pat. No. 4,246,365 teaches that the fire resistance of polyisocyanurate foams can be improved by using polyester polyols based on phthalic acid residues. U.S. Pat. No. 4,039,487 teaches a wide variety or aromatic polyester polyols which are said to produce foams With good ASTM E-84 performance.
In an article entitled "The Use of a Unique Aromatic Polyester Polyol in Urethane Modified Isocyanurate Foam Systems" (SRI ANTC, pages 348-351, R. J. Wood, 1983), the use of aromatic polyester polyols combined with various polyethers, solubilizers and relatively low viscosity polyisocyanates is described.
The use of aromatic polyester polyols in combination with sucrose or sucrose-amine based polyethers and low viscosity polyisocyanates is disclosed in U.S. Pat. Nos. 4,459,334 and 4,496,625, and in "New Polyols for Urethane Modified Isocyanurate Foams" (Journal of Cellular Plastics, May-June, 1984, K. B. White et al, pages 215-219). Polyester polyols which are based on aromatic acids, diethylene glycol and propylene glycol are known (See e.g., Technical Data Bulletin-Firemaster PHT 4-diol.)
Polyester polyols which are the reaction products of polyalkylene terephthalate or recycled polyethylene terephthalate (PET) or dimethyl terephthalate (DMT) with various glycols or glycol blends are also known. Such polyols are disclosed in U.S. Pat. Nos. 4,048,104; 4,223,068; 4,100,354; 4,506,090; 4,436,229 and 4,411,949. Systems based on those polyester polyols Which are produced by reacting a polyalkylene terephthalate residue (PET) with glycol (U.S. Pat. No. 4,417,001) and transesterified dimethylterephthalate oxidation residue (U.S. Pat. Nos. 4,237,238; 4,394,286 and 3,647,759) are also known. Polyurethane foams prepared using such polyester polyols exhibit lower flamespread and smoke generation ratings than corresponding foams prepared without such polyols when evaluated in accordance with ASTM E-84.
Urethane modified polyisocyanurate foams made from polyester-containing polyol blends in which the fire retardance performance is acceptable only at a density of about 2 pounds per cubic foot or below are described in U.S. Pat. Nos. 4,521,611; 4,526,908 and 4,544,679.
U.S. Pat. No. 3,637,542 discloses fire-retardant polyurethane foams having reduced smoke levels. The invention comprises incorporating adipic acid into the fire retardant foam formulation as the smoke reducing agent. Similarly, U.S. Pat. No. 3,639,307 describes incorporating fumaric acid into a fire-retardant foam formulation as a smoke reducing agent. U.S. Pat. No. 4,060,173 describes the use of cyclic polycarboxylic acids as smoke reducing agents in polyurethane/polyisocyanurate foams. U.S. Pat. No. 4,797,428 discloses rigid flame resistant polyurethane foams made by reacting an aromatic polyisocyanate with a mixture of 25-75% oligoester and another isocyanate reactive material, wherein the oligoester is the reaction product of a dicarboxylic acid ester or amide and an alkylene oxide. Such foams attain an ASTM-E84 Class I flame rating.